The standard procedure used to prepare a mask for fabrication of microwave circuitry consists of using a two layer polyethylene terephthalate (Mylar) film -- one layer is photographically opaque, the other layer is translucent. The desired circuit is hand cut to required dimensions. The circuit outline is cut through the opaque layer of film and the unwanted portions are then removed from the surface. A single mask for each circuit is required. The mask designs are in different configurations depending on the frequency used, and the type of circuit desired. Accuracy is of prime importance in the preparation of these masks. If an existing mask needed modification in one or more given measurements an entirely new mask had to be cut. In cutting a new mask only slight differences in previously acceptable mechanical measurements results in another variable that must be dealt with to obtain the desired pattern. The method described herein utilizes one mask and redundant use to provide accurate fabrication of apertures for microwave circuits.